1.1 Advice about using rewrite rules

Remember to use the flag -fglasgow-exts and the optimisation flag -O

Use the flag -ddump-simpl-stats to see how many rules actually fired.

For even more detail use -ddump-simpl-stats -ddump-simpl-iterations to see the core code at each iteration of the simplifer. Note that this produces lots of output so you'll want to direct the output to a file or pipe it to less. Looking at the output of this can help you figure out why rules are not firing when you expect them to do so.

You need to be careful that your identifiers aren't inlined before your RULES have a chance to fire. To control this we add an INLINE [1] pragma to identifiers we want to match in rules, to ensure they haven't disappeared by the time the rule matching comes around.